A quantum-dot based avalanche photodiode (qd-APD) may include a silicon substrate and a waveguide on which a quantum dot (qd) stack of layers is formed having a qd light absorption layer, a charge multiplication layer (CML), and spacer layers. The qd stack may be formed within a p-n junction. The waveguide may include a mode converter to facilitate optical coupling and light transfer from the waveguide to the qd light absorption layer. The qd absorption layer and the CML layer may be combined or separate layers. The CML may generate electrical current from the absorbed light with more than 100% quantum efficiency when the p-n junction is reverse-biased.
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1. A quantum-dot based avalanche photodiode (qd-APD), comprising:
a waveguide to receive light;
a quantum dot (qd) stack of layers formed on top of the waveguide and deployed in a middle of a semiconductor p-n junction to receive light from the waveguide and generate an electric current with greater than one hundred percent (100%) internal quantum efficiency when the semiconductor p-n junction is reverse-biased; and
a mode converter to couple the light received by the waveguide to the qd stack of layers.
15. A quantum-dot based avalanche photodiode (qd-APD), comprising:
a waveguide to receive light;
a quantum dot (qd) stack of layers formed on top of the waveguide and including:
a plurality of qd and charge multiplication layers (qd-CML) within a semiconductor p-n junction, the plurality of qd-CML to absorb light and to multiply electrical charges with greater than one hundred percent (100%) quantum efficiency in response to the light absorbed when the p-n junction is reverse-biased, and
a plurality of spacer layers to separate the plurality of the combined qd-CML.
8. A quantum-dot based avalanche photodiode (qd-APD), comprising:
a waveguide to receive light;
a quantum dot (qd) stack of layers formed on top of the waveguide and including:
a plurality of qd light absorption layers within a semiconductor p-n junction to absorb light, the plurality of qd light absorption layers separated by spacer layers, and
a charge multiplication layer (CML) to multiply electrical charges with greater than one hundred percent (100%) internal quantum efficiency in response to the light absorbed when the semiconductor p-n junction is reverse-biased.
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20. The qd-APD of
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This invention was made with Government support under Agreement Number H98230-18-3-0001. The Government has certain rights in the invention.
Optical systems may be used to manipulate optical signals in various ways. For example, photodetectors may absorb an optical signal and convert it into an electrical current. As another example, laser diodes may be used to generate lasers by applying a voltage across the diode's p-n junction to make it forward-biased.
The following detailed description references the drawings, wherein:
The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar parts. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only. While several examples are described in this document, modifications, adaptations, and other implementations are possible. Accordingly, the following detailed description does not limit the disclosed examples. Instead, the proper scope of the disclosed examples may be defined by the appended claims.
The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The term “coupled,” as used herein, is defined as connected, whether directly without any intervening elements or indirectly with at least one intervening elements, unless otherwise indicated. Two elements may be coupled mechanically, electrically, or communicatively linked through a communication channel, pathway, network, or system. The term “and/or” as used herein refers to and encompasses any and all possible combinations of the associated listed items. It will also be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms, as these terms are only used to distinguish one element from another unless stated otherwise or the context indicates otherwise. As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on. The terms “about” and “approximately”, used interchangeably, mean up to 5% variation (plus or minus) from a given quantitative value following these terms. The term “adjacent,” when applied to two components, regions, or layers, means no other components, regions, or layers, respectively, are physically interposed between the two components.
Optical systems generally Include at least two types of components, those that generate or emit light, such as lasers, and those that detect light, such as photodetectors. Depending on the functions of the optical systems, the light transmitted within the system may represent a signal with certain predefined semantics, or represent optically encoded data. An example of light as a signal is an optical alarm system which may detect light or lack thereof and interpret the signal as an alarm that a restricted area has been breached. Examples of light as encoded data include fiber optic systems used in high-performance computer systems and wide-area or local-area optical networking, which use optical media or links to carry encoded digital data from one source computer or storage to another one. When light is used to carry data, the integrity of the data depends on the quality and sensitivity of light detection because unreliable detection of optical data may result in unreliable data (for example, a false positive or a false negative mistaking binary 1 for binary 0 or vice versa). Accordingly, a highly sensitive light detector may reduce data error, reduce power consumption, increase data density and bandwidth, and provides other benefits as further described below. A QD-APD device may be used to solve some or all of these problems.
Examples disclosed herein describe a QD-APD as a highly sensitive optical detector that may be built on a silicon waveguide to create a highly sensitive light detector. This may be done by creating or forming multiple layers on the passive silicon waveguide including one or more quantum dot (QD) light absorption layers and zero or more charge multiplication layers (CML), alternating with separator layers. In some example implementations, the QD light absorption and CML layers may be combined into one layer. A QD-APD includes three distinct sections along its length. One section is a silicon waveguide section, a second section is a mode conversion transition section, and a third section is a QD section in which the QD/CML is located. Light first enters the silicon waveguide section, then crosses the mode conversion transition section in which the silicon waveguide tapers down and becomes narrower, and the light absorption layer starts small and narrow and then gradually widens and becomes wider. At this point, in the QD section, the avalanche effect takes place.
The QD/CML layers may be reverse-biased to create an avalanche mode of operation with greater than 100% internal quantum efficiency. Internal quantum efficiency excludes the efficiency of the mode converter, described later in detail. In such configuration, one photon creates an electron-hole pair in the absorption layer. Hence, the output from one photon entering the QD-APD is greater than one charged particle (electron or hole). This allows a small amount of light to create a large and usable electrical current (signal) for electronic processing by a circuit or a computer.
Some example implementations described herein disclose a QD-APD operating in avalanche mode with gains resulting in internal quantum efficiencies greater than 100%, as further described below. This type of high-efficiency photodetector may detect minute amounts of light, compared with other implementations.
In some example implementations, the QD-APD includes several layers of QDs separated by spacer layers of material such as Gallium Arsenide (GaAs), and separate CML layers deposited near P-cladding in some examples, or N-cladding in other examples.
There are several advantages provided by such high-efficiency photodetection. One advantage is the output power of a laser can be reduced, thus increasing the efficiency of the optical link.
Another advantage of QD-APDs is that they have inherent gain due to their avalanche mode behavior. Hence, a QD light absorption layer may act as an electrical signal amplifier.
Still another advantage of QD-APDs and a solution to some manufacturing complexity problems is that the same material stack as a diode laser may be used to manufacture the QD-APD. The same design and manufacturing techniques may be used to manufacture both the QD-APDs and QD comb laser and ring laser devices resulting in high-performance photodetectors and lasers. More specifically, simple integration of lasers and photodetectors manufactured this way, using a single bonding step with no selective area bonding, and no high temperature growth steps is possible. Hence, in the same manufacturing process, different devices may be manufactured less expensively that may be integrated more easily in various applications.
Another advantage of QD-APDs integrated on silicon described herein is efficient coupling between passive silicon waveguides, which reduces cost and complexity of systems and system data interfaces.
Still another advantage of QD-APDs is lower dark current than bulk or quantum well photodetectors. Dark current is the random charges, or electric current, generated inside the photodetector without any input light. It is due to random charge generation and recombination of electrons and holes. Dark current is generally not desirable because it distorts the output current or signal of the photodetector and may also result in a false output signal. Dark current in a QD-APD is less sensitive to etching defects and high temperatures in usage.
Turning now to the drawings,
In some example implementations, the laser device 102 may be a comb laser generating multiple carrier light beams each at a different frequency, or equivalently, a different wavelength. Data may be modulated onto the carrier light beams via the modulators 104. Each of the modulators 104 modulates a different data stream and encodes it onto a different carrier beam. Those skilled in the art will appreciate that a data stream is a series of related data belonging to one data set and serially following each other from a source to a destination. This way, the same optical media, for example, the optical fiber 103, may carry multiple data streams simultaneously without interfering with each other. For short distances, for example on the order of a few inches, the media used may not be a solid or even a material medium but air or a vacuum.
The receiver 105 may receive the modulated carrier beams and then demultiplex them via the demultiplexing rings 106, each demultiplexing ring 106 being tuned to a particular frequency of carrier beam. Thus, each demultiplexing ring 106 in effect filters and separates the carrier to which it is tuned from the multiple streams multiplexed together in the optical fiber 103. The demultiplexing rings 106 are further coupled with QD-APDs 107 that receive a particular frequency of light and convert them, along with the data modulated onto the carrier. This process is further described with respect to
In some example implementations, the passive waveguide 201 may be made of silicon, which may also function as a substrate for other layers, as further described below. The passive waveguide 201 tapers down in the proximity of the QD stack 203 widening. The taper angles with respect to Y-axis may be between about 1° and about 90°. This proximity where the dual tapers take place forms the mode converter 202 in which the light is directed to the QD stack 203 from the passive waveguide 201, as further described with respect to
With continued reference to
Light absorption in the QD stack 203, further described below, and charge amplification may occur in the same epitaxial layer, in some example implementations, and may happen in different epitaxial layers in other example implementations. As described later in more detail with reference to
According to one or more implementations,
Continuing on to the second cross-section of the three QD-APD 200 sections, according to one or more implementations,
With reference to
Now, with reference to
With reference to
With reference to
The maximum quantum efficiency of non-avalanche mode of operation is 100%, indicating that each photon 312 (considered as an input to the p-n junction) generates at most one electron-hole pair as the electrical charge (considered as an output from the p-n junction).
, may be generated by the laser device, for example, a comb laser, and combined and transmitted over one optical media, such as an optical fiber 103. A wavelength vs. power graph 402 shows several distinct carriers with different wavelengths 403 being transmitted via a waveguide 401. A number of ring waveguides 404a-404d each having a different radius R1-R4, respectively, are coupled with the waveguide 401 via evanescent coupling through small air gaps 408a-d, respectively, on the order of about 0.2 μm or more or less as desired. The waveguide rings 404a-404d are further coupled with QD-APD waveguides 405a-d, via other air gaps 407a-407d, respectively. Each of the QD-APD waveguides 405a-d receives the corresponding data stream with distinct carrier wavelengths 406a-d, from the respective waveguide rings 404a-404d.
Optical evanescent coupling is used to transfer light between an optical transport, such as a waveguide, to semiconductor devices, such as photodetectors that use or process the light. The waveguide rings 404a-404d inherently operate in a narrow bandwidth by resonance. As a result, the rings may be tuned to particular frequencies. In practice, the tuning is done by choosing the appropriate radius for the waveguide rings and can be further fine-tuned by a heater and/or a MOS-tuner (metal oxide semiconductor tuner). This way, each ring separates a particular carrier with the frequency tuned to the radius of the ring, which is subsequently passed on to the corresponding QD-APD waveguide.
1 and
2 via air gaps 503a and 503b, respectively. The demultiplexing tuning ring waveguides 502a and 502b are in turn coupled with QD-APDs 505a and 505b via air gaps 504a and 504b, respectively.
With this arrangement, each of several optical signals transmitted by optical media, such as an optical fiber, are separated by the demultiplexing tuning ring waveguides 502a and 502b and transferred to the appropriate QD-APD for detection and subsequent electrical charge generation.
In this arrangement, the tuning ring waveguide 603 is implemented as a QD-APD and performs both the function of tuning and separating the optical signal from the waveguide 601 and the function of detecting the light signal. This way the optical data transmission system may be simplified and be produced at lower cost.
In this arrangement, the tuning ring waveguide 703 is implemented as a QD-APD and performs both the function of tuning and separating the optical signal from the waveguide 701 and the function of detecting the light signal. This way the optical data transmission system may be simplified and be produced at lower cost.
The foregoing disclosure describes a number of example implementations of a QD-APD. For purposes of explanation, certain examples are described with reference to the components illustrated in
Zhang, Chong, Huang, Zhihong, Liang, Di, Zeng, Xiaoge, Beausoleil, Raymond, Kurczveil, Geza, Tossoun, Bassem
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